Flux is used in the field of soldering, silver brazing, electric welding and so on to improve soldering by removing oxides on the surface of metal substrates, preventing re-oxidation during heating, or lowering the surface tension of solder to increase wetting property.
The flux is a composition containing a resin, an activator and other additives. Conventionally, flux comprising a rosin as a main ingredient is used in the electric and electronic fields in which flux residues are not washed after soldering. However, when the flux is used for soldering of important security parts such as precision electronic parts, electric equipment for automobile, and so on, flux residues must be removed by washing. Therefore, when a rosin-type flux is used, fluorine-based organic solvents or chlorine-based organic solvents that fully dissolve the rosin have been used for washing after soldering. However, these organic solvents become strictly regulated as they have adverse influence on safety and sanitation, and global environment. Thus, it is desired to minimize the use of them. Consequently, flux compositions that dissolve in water or warm water get a lot of attention for removing flux by washing after soldering.
On the other hand, the metals used for solder itself are also becoming a subject to regulation. Although the metals used for the conventional solder material were mainly tin-lead based ones, much attention is directed to lead-free solder in order to reduce the effects on the environment. Further, in Europe, “Restriction of the use of hazardous substances including lead (RoHS Directive)” will be enforced from July of 2006, and much attention is directed to lead-fee solder also from world point of view. As lead-free solders, tin-silver-copper based, tin-silver based ones, and so on are known, but they have a higher melting point by 20 to 30° C. than the conventional tin-lead based one. Therefore, also for the flux composition used in soldering, heat resistance is required, it is desired to develop flux compositions having heat resistance together with the above-mentioned water soluble property.
A flux composition for soldering containing a polyester polycarboxylic acid synthesized from an esterification reaction of a polyol with a polycarboxylic acid is disclosed as a flux for reducing soldering defects. The polyol includes ethylene glycol, several epoxy resins, and the polycarboxylic acid includes (anhydrous) succinic acid, (anhydrous) phthalic acid, and the like (Patent Document 1).
A flux composition for solder in which at least one of vinyl group-containing compounds, carboxyl group-containing compounds, and epoxy group-containing compounds, and a modified amine compound obtained by a reaction of an amine compound having active hydrogen are used as flux base resins is disclosed. The carboxyl group-containing compounds include acetic acid, citric acid, and the like, the amine compound having active hydrogen includes n-propylamine, ethylene diamine, and the like. The modified amine compound is a compound obtained by condensation reaction of an active hydrogen-containing amine compound with a carboxyl group-containing compound. The flux composition containing these modified amine compounds can contain organic acids such as benzoic acid, succinic acid, maleic acid, and the like. (Patent Document 2).
A water soluble flux composition for solder containing a resinous substance being a reaction product of one or two or more carboxyl group-containing compounds selected from the group consisting of monocarboxylic acid, polycarboxylic acid and hydroxycarboxylic acid having carbon atom number of 8 or less, with tris-(2,3-epoxypropyl)-isocyanurate, and an activator is disclosed. The carboxylic acid includes acetic acid, oxalic acid, succinic acid, citric acid, and the like, and the activator includes lactic acid, oleic acid, aniline hydrochloride, ethylene diamine, and the like (Patent Document 3).    Patent Document 1: JP-A-4-200992 (1992) (Claims)    Patent Document 2: JP-A-5-008085 (1993) (Claims)    Patent Document 3: JP-A-3-018498 (1991) (Claims)